An example of a cutting insert of the above specified kind is a drilling insert of a trigon shape, each cutting edge of which extends between two adjacent insert corners and comprises two component cutting edges meeting at an intermediate corner which, as seen in the insert plan view, protrudes beyond an imaginary line connecting the adjacent insert corners.
When the cutting insert is mounted in a tool, the intermediate corner of its operative cutting edge protrudes in an axial direction of the tool, whereby it is ensured that, during cutting, the intermediate corner is the first to contact a workpiece being cut. This enables the intermediate corner to perform a so-called piloting function.
However, with the intermediate corner protruding in the axial direction, the planarity of a workpiece face surface being cut is very poor. This makes the inserts of the above design non-suitable for cutting operations where high degree of planarity of a workpiece face is required.
It is the object of the present invention to provide a new cutting insert which allows for a high planarity of a workpiece face surface machined thereby and provides for a `piloting` effect.